The production of liquefied gas offshore by production and liquefaction of natural gas requires the transfer of the liquefied gas between floating units or seabed based offshore units, between one seabed based offshore unit and one floating unit. Concepts for offshore transfer system between two units usually involve the use of heavy lifting cranes, and complex systems including hydraulics, position control, ship movement compensation, and a large number of parts. It is also important to avoid clashes between the different conduits spaced closely together. This is especially the case for current ship to ship transfer systems suitable for LNG, which must be maintained at a temperature of −163° C. Therefore, current concepts are very heavy and expensive, operator unfriendly, difficult to maintain, and prone to failure. All existing transfer concepts are not ideal to be used in harsh environment and harsh sea state.
In this patent application, a preferred offshore transfer system configuration would be a tandem offloading configuration between two vessels. In a tandem offloading configuration the carrier will position itself in line behind the process vessel or FPSO (Floating Production Storage and Offloading unit). The position will be in-line with the current since the FPSO will weathervane. In between the FPSO and carrier, a hawser line will be holding the carrier at a certain distance from the FPSO. To insure that the carrier will not clash with the FPSO, back trust should be provided by the carrier.
In a tandem offloading configuration, it is also required to have means that will allow one or more offloading hoses to be lowered into the sea and will provide buoyancy at the end fitting locations, but also means to transport offloading hose(s) in the vicinity of the carrier. Further, one or more hoses (floating or submerged) needs to be lifted up from water level to a certain height, for example the vessels deck, which could be 10-30 m above water level, to be connected to a fluid piping manifold. The use of local cranes and/or winches is not always possible as the overall weight of the hose(s) to be lifted up is too large, because the lifting capacity is limited, or they are not located at the required/needed place on the deck. Moreover, installing additional lifting equipment or modifications on existing lifting systems onboard carriers is not a preferred solution, as it needs to be done on each carrier that must be connected to the hoses.
A solution that avoids any additional modifications to be made on board the carriers is advantageous as it can be used for any standard carrier.
The proposed system, manufactured under the trademark CryoRide™ by the applicant, is a key system to enable an easiest, fastest and cheapest offloading connection between two offshore units.
In this patent application the term “transfer hose” is used to designate all types of transfer hoses which are suitable for the transfer of hydrocarbons, in particular cryogenic fluids (at −163° C.) but also for the transfer of liquefied gas such as LPG and liquefied CO2.